1. Field of the Invention
The invention relates to an image forming apparatus such as printer or the like.
2. Related Background Art
An image forming apparatus with electrophotography is formed from an image carrying body which is formed in a developing device and is used to form an electrostatic latent image; a transferring roller which is placed to face to the image carrying body and is supplied a transfer voltage by a voltage supplying section; a transferring belt which is made out of member having a definite electrical resistance and is used to convey record medium; a driving section for transferring device to drive the transferring belt; and a fixing device which is used to fix developer onto the record medium conveyed by the transferring belt.
When the image forming apparatus received image information from outside, the image forming apparatus makes the surface of the image carrying body be on charge; forms an electrostatic latent image on the surface of the image carrying body by an exposing device based on the image information; forms a developer image on the image carrying body on which the electrostatic latent image is formed by supplying developer such as toner filled in a cartridge to the image carrying body formed in developing device; transfers the developer image onto record medium by using the image carrying body and the transferring roller; and forms an image onto the record medium by making the fixing device to fix transferred developer.
In such image forming apparatus, while forming the developer image on the image carrying body, a remainder quantity of the developer is calculated by measuring a consumption of consumed developer. Such technology is disclosed by patent document 1.
Patent document 1: Japan patent publication 2002-283675.
In the patent document 1, in the concrete, picture element number to constitute the image information inputted into the exposing device is counted; a unit quantity of the consumed developer for one picture element is previously set; a developer consumption is calculated by using a proportional relation between the unit quantity per picture element and the picture element number to constitute the image information; and the developer consumption is recorded cumulatively. A difference between a developer initial quantity accommodated in an unused cartridge and the developer consumption cumulatively recorded serves as a remainder quantity of the developer in the cartridge.
However, with long time use, the electrical characteristic of the surface of the image carrying body falls, and the electric potential distribution in neighborhood of border between exposure portion and un-exposure portion on the surface of the image carrying body is not steep but becomes some flat. Therefore, while developing image, a phenomenon called fog happened, that is, a trace of the developer sticks to the portion on which image should not be formed. On the contrary, another phenomenon also happened, that is, the developer does not stick to the portion on which image should be formed. When such phenomenon happens, the proportional relation between the unit quantity per picture element and the picture element number to constitute the image information is not valid, an error happens between the cumulative developer consumption calculated on the basis of the image information inputted into the exposing device and the actual developer consumption. If such phenomenon often happens, the error will enlarge.